7. Resources and Eutrophication D4.2

Stability & Change in Ecosystems

Guiding Question

• "What changes caused by humans threaten the stability of ecosystems?"

D4.2.1 Stability as a Property of Natural Ecosystems

• Ecosystem Stability Illustration

  • Evidence of ecosystems like forests and deserts showing continuity over millions of years.

D4.2.2 Requirements for Stability in Ecosystems

• Essential components include:

  • Supply of Energy: Necessary for organism survival and ecosystem functioning.

  • Recycling of Nutrients: Nutrient cycling is vital for maintaining ecosystem productivity.

  • Genetic Diversity: Ensures resilience against changes and stressors.

  • Climatic Variables: Must remain within tolerance levels to avoid disrupting ecosystems.

D4.2.3 Deforestation of the Amazon Rainforest

• Tipping Point in Ecosystem Stability

  • Rainforests play a crucial role in generating atmospheric water vapor through transpiration, impacting cooling, air flows, and rainfall patterns.

  • Uncertainties exist regarding the minimum rainforest area necessary to sustain these processes.

D4.2.4 Mesocosms and Ecosystem Variables

• Mesocosm Setup:

  • Preferably done in sealed glass vessels to prevent matter entry and exit while allowing energy transfer.

  • Aquatic or microbial ecosystems are generally more successful than terrestrial ones.

  • Maintain care and follow IB experimental guidelines for mesocosm maintenance.

D4.2.5 Keystone Species and Ecosystem Stability

• Role of Keystone Species:

  • Disproportionate impact on community structure.

  • Significant risk of ecosystem collapse when keystone species are removed.

D4.2.6 Sustainability of Resource Harvesting

• Sustainability Definition:

  • Rate of resource harvesting should be lower than the rate of replacement to maintain ecological balance.

• Examples:

  • Renewable Resources: Include both terrestrial plant species and marine fish.

D4.2.7 Factors Affecting Sustainability of Agriculture

• Critical considerations include:

  • Soil erosion

  • Nutrient leaching

  • Input supplies such as fertilizers

  • Pollution from agrochemicals

  • Carbon footprint associated with farming practices.

D4.2.8 Eutrophication of Aquatic and Marine Ecosystems

• Impact of Eutrophication:

  • Resulting from nitrogen and phosphate leaching, leading to increased biochemical oxygen demand (BOD).

D4.2.9 Biomagnification of Pollutants

• Concept of Biomagnification:

  • Toxins accumulate in consumer tissues at higher trophic levels.

  • Examples include DDT and mercury.

D4.2.10 Pollution from Plastics

• Plastic Impact:

  • Both microplastics and macroplastics are persistent in the environment due to non-biodegradability.

  • Negative effects on marine life due to plastic pollution.

D4.2.11 Restoration through Rewilding

• Methods of Restoration:

  • Reintroduction of apex predators and keystone species.

  • Re-establishing habitat connectivity over large areas.

  • Minimizing human impact through ecological management, e.g., Hinewai Reserve in New Zealand.

Sustainability in Resource Harvesting

• Long-term Viability:

  • Sustainability is essential for ensuring future conditions remain conducive for ecosystems.

Resource Harvesting Examples

• Forests in Finland: Historically significant for food, shelter, and income. Laws require regeneration after logging.

• Cod Overfishing: The North Atlantic Cod is on the brink of extinction due to overfishing; highlights the need for sustainable fishing practices.

Eutrophication Process Overview

• Eutrophication Definition: A process characterized by excessive nutrient enrichment in water bodies, leading to algal blooms.

• Impact on Aquatic Ecosystems:

  • Algal blooms block sunlight, inhibiting photosynthesis of underwater plants.

  • Resulting high BOD levels can be detrimental to aquatic health and biodiversity.

Measuring Biological Oxygen Demand (BOD)

• BOD Measurement Process:

  • Initial oxygen content measured, then placed in the dark for 5 days.

  • Final measurement reflects oxygen depletion caused by organic material breakdown, indicating water quality.